Agriculture products are often fumigated to control pests, including insects, plant pathogens, weeds, mollusks, nematodes, vertebras, and microbes that can destroy property, cause nuisance, spread disease or are vectors for disease.
Psyllium and other grains are often fumigated with methyl bromide, which is an effective fumigant since it is highly toxic to most pests. However, methyl bromide can create residual inorganic bromide in the fumigated products. USP <561> has established that 50 ppm is the maximum amount of inorganic bromide residue that can be in or on grains, such as psyllium. 
When processing psyllium, including psyllium husk, it can be difficult to fumigate with enough methyl bromide that the pests, especially the khapra beetle and other insects, are destroyed while maintaining a level of inorganic bromide residue that is less than 50 ppm. The USDA recommends treating grains not for propagation with a minimum of 40 g/m3 of methyl bromide at 21° C. or greater. However, when this level is used with psyllium the fumigation can result in inorganic bromide residue that is greater than 50 ppm, which results in psyllium that does not meet compendia and must be discarded.
There is a need for an effective method to fumigate psyllium, including psyllium husk, with methyl bromide where the fumigated psyllium comprises less than 50 ppm inorganic bromide residue.